I developed a mass email system, much like phpList, for World Council of Credit Unions (WOCCU) as one of my first projects for them 5 years ago. It was developed to manage email lists that can cross pollinate in our custom content management system (CRM). One thing that was overlooked and disregarded was what to do with bounced emails. Previously, it was the responsibility of the sender to clean the lists but that was ineffective and slow. To fix this issue I took some development time and created a system that went into a shared bounce email account, grabbing all the bounced emails and applying various flags to contacts in the CRM. The system manages to figure out why an email bounced (no small feat), as well as what mass email created the issue and which contacts should be fixed.